1. Field of the Invention
The present invention relates to a vehicle control device.
2. Description of the Related Art
A vehicle control device that is mounted on a vehicle, which includes an engine with a supercharger and an automatic transmission coupled to the engine, and that controls an air-fuel ratio of the engine according to an operation state of the engine to switch a combustion mode is conventionally known (see e.g., Japanese Patent Application Laid-Open No. 2009-144575 and Japanese Patent Application Laid-Open No. 2006-300253).
Among the various combustion modes, a necessary intake air amount is large in a lean combustion mode (hereinafter described as a supercharged lean combustion mode), in which supercharging is executed by a supercharger, compared to the other combustion modes (e.g., stoichiometric combustion mode), in which the air-fuel ratio is an air-fuel ratio on a rich side than the air-fuel ratio in the supercharged lean combustion mode. In other words, when switching to the supercharged lean combustion mode from another combustion mode, the supercharging pressure needs to be raised to a required supercharging pressure required in the supercharged lean combustion mode.
If an up-shift of a change gear ratio in the automatic transmission is executed when switching to the supercharged lean combustion mode from another combustion mode, an engine rotation number decreases with the execution of the up-shift and hence the rise of the supercharging pressure may be delayed. In other words, in the case described above, the transition to the supercharged lean combustion mode is delayed and the other combustion mode is maintained, and consequently, the fuel efficiency lowers.